Answering Questions- around 100 words

I’m studying for my Chemistry class and don’t understand how to answer this. Can you help me study?

watch the video

answer the question .

Questions that arise: Why does the dollar dominate trade even though alternate currencies are available (Euro, GBP, Yen and now Yuan(Renminbi). More so in swaps – when it should not really matter – Euro or GBP or Yen can be far more significant? What may explain it?